When I switched my iMac on this morning, I went to the other side of the room to gather some paperwork and as I was doing so, I heard a microwave-like beep come on during the user login screen. It was only a fraction of a second long and didn't repeat, but it has concerned me. I know that these iMacs beep for RAM issues, so I tested the RAM firstly by trying to utilize all of the RAM which seemed successful, then with TechTool Deluxe and finally with Memtest, both of the latter are showing that RAM is okay, but I will continue testing throughout the day in different modes and so on. My question is, could this be anything serious? What could the single beep mean; just a glitch or something worse. Any help would be greatly appreciated, thank you.